1. Field of the Invention
The present invention relates to a method of treating waste materials which contain radioactive isotopes of cesium. More specifically, the instant invention concerns a method of treating waste material, usually liquids, which is contaminated with cesium isotopes to thereby contain or control the mobility of such cesium isotopes when the so-treated waste material is exposed to the leaching action of an aqueous environment.
2. Description of the Prior Art
In the nuclear field, for example in the generation of electric power by means of a nuclear reactor, cooling fluids are used which occasionally become contaminated with various radioactive substances. Obviously, a means must be provided for preventing these materials from coming into contact with the general environment.
To date, various techniques have been developed in an attempt to obviate this problem. For example, in the treating of liquids which are contaminated with radioactive materials evaporation, carrier precipitation (coagulation), sand filtration, ion exchange (including natural clays), electrodialysis, metallic displacement or scrubbing, solvent extraction, biological processes and crystallization have all been utilized. While these techniques have experienced varying degrees of success, they all suffer for one common defect in that all of the radioactive contamination cannot be removed from the liquid being treated.
Presently, when it is desired to contain or immobilize all of the radioactive contamination found in a waste material, the waste material is solidified if it is in a liquid state and encapsulated if it is in the form of a solid.
In the treatment of liquids, the waste is put into a containing vessel and then solidified by the addition thereto of a material such as Portland cement. The same general procedure is utilized to treat solid waste material. That is, it is positioned in a container and subsequently encapsulated by the addition thereto of a cementitious potting material.
Containers of the above described type are then taken to an interim storage area, which may be above or below ground level, or buried permanently in an approved land fill. While this is generally a highly effective way of containing radioactive waste material, it is not entirely satisfactory in certain circumstances. For example, if the solidified or encapsulated waste material contains radioactive cesium isotopes, especially cesium 137, and it eventually comes into contact with an aqueous environment there is a tendency for the cesium to be leached out of the treated waste material. These radioactive cesium isotopes then contaminate the surrounding area.
Various attempts have been made to reduce the leachability of radioactive cesium isotopes from solidified waste material of the above described type. For example, such materials as Grundite, (an illite type of clay), pottery clay and Conasauga shale have all been added to various grouts used to solidify isotopes which might be present. While such additives did reduce the leachability of such isotopes to some degree, they did not do so in a completely satisfactory manner. That is, undesirable amounts of cesium still can be leached out of such solidified materials when they are contacted by an aqueous leachant.
In addition, a relatively new technique described in U.S. Pat. No. 3,841,102 for improving the quality of leachate from sanitary landfills has also been evaluated as a means of immobilizing radioactive cesium isotopes found in certain liquid wastes. In the use of this technique, cement and an alkali metal silicate are used to solidify the waste material. However, while this approach has met with some limited success, it still has not resulted in a system which immobilizes radioactive cesium isotopes to a desirable degree. That is, radioactive cesium isotopes are still easily leached from so-treated and solidified waste material.
Accordingly, it is the principal object of the invention to overcome the difficulties experienced by prior art means for treating waste material which is contaminated with radioactive cesium isotopes.
Other objects of the invention will become apparent to those skilled in the art from a reading of the specification and claims.